Producing textile fibres from wood involves extracting cellulose from a structure that is tougher and more resistant than that of grass. But what if grass offered an easier – and potentially more environmentally friendly – alternative? Researchers at Chalmers University of Technology have produced dissolving pulp from grass and clover residues. Working with collaborators, they have also spun the pulp into fibres and knitted a small fabric sample. The results open up new possibilities for turning agricultural residues into valuable materials.
Researchers at Chalmers have produced dissolving pulp from grass and clover residues. Together with collaborators, they have also spun textile fibres and knitted a small fabric sample. Pictured: Diana Bernin (top) and Leandro Cid Gomes (bottom). The illustrations are taken from the researchers’ scientific study, published in ACS Sustainable Chemistry & Engineering.
When protein is extracted from grass and clover, a fibre-rich residue known as press cake remains. It contains cellulose, the same substance used to produce textile fibres from wood.
“The cellulose is the same whether it comes from a tree or from grass. The difference is how easily we can extract it,” says Diana Bernin, Associate Professor at the Department of Chemistry and Chemical Engineering at Chalmers.
Together with postdoctoral researcher Leandro Cid Gomes, she has investigated how the cellulose in press cake can be put to use. He is also the lead author of the scientific paper presenting their findings: Green Biorefinery Side Stream as a Source of Chlorophyll Pigments, Lignin, and Cellulose for Textile Fibers.
The same cellulose – but easier to extract
Trees are built to withstand the elements for many years. This also makes their cellulose more difficult to extract. In grass, the cellulose fibres are more accessible.
“We can use simpler chemistry and smaller amounts of chemicals to extract the fibres. This also saves energy,” says Diana Bernin.
However, the extent of the potential environmental and resource benefits remains uncertain.
“The environmental and resource benefits need further investigation. We have worked with a process on a laboratory scale, and it is difficult to compare that with an industrial-scale process. The next step is to test the process at pilot scale and compare it with a large-scale industrial process.”
From press cake to knitted fabric
Diana Bernin's research group has previously worked with other agricultural residues, including wheat straw and oat husks. Now the researchers have also succeeded in producing cellulose pulp from the press cake left after processing grass and clover.
“We have produced pulp from the press cake, which is initially brown and green, and shown that it meets the requirements for dissolving pulp, including purity. In collaboration with Aarhus University and the Swedish School of Textiles in Borås, we have been able to spin fibres from our pulp and even knit a small sample using those fibres.”
But why focus on textiles?
“Our aim has been to produce something of high value, and that is where textile fibres come in. Packaging could also be an option, but it would be much better to make a product that can be used for a long time and potentially recycled.”
Part of a wider research effort
Producing textile fibres from grass and clover is one of several possibilities being explored in research on green biorefineries. The aim is to make better use of different parts of the plants while developing agricultural systems that use land and resources more sustainably.
In the Swedish-Danish Green Valleys project, researchers, farmers and other stakeholders have worked across the entire value chain – from cultivation and harvesting to protein extraction, biogas production and other bio-based products. Two demonstration facilities, one at Sötåsen Agricultural College in Sweden and the other at Aarhus University in Denmark, have made it possible to test the technology in practice.
Chalmers researchers Christel Cederberg and Göran Berndes, whose work we have previously reported on, have investigated how grass and clover cultivation affects agricultural land, the potential environmental benefits, and how different uses of the biomass influence resource requirements.
An important question is what happens to the press cake once the protein has been extracted. So far, it has mainly been used for biogas production, but it could also provide raw materials for new products.
Diana Bernin's research group was not formally part of Green Valleys. However, the group is now continuing its work on cellulose within Land2Value, a follow-on project involving additional partners, including researchers from Norway.
More products – but can the processes be combined?
Could material extraction and biogas production be combined to make better use of the press cake? That remains to be investigated.
“Hmm, good question! We haven't looked into this, but it would of course be great if we could obtain several products. In our scientific paper, we have also shown that lignin and the pigment chlorophyll can be extracted from the press cake. But I unfortunately can't say whether this can be combined with biogas production. Press cake contains more than just cellulose. Our aim is to recover as many useful molecules as possible.”
From laboratory to textile production
Producing cellulose pulp is one thing. Turning it into textile fibres is another. Although cellulose is easier to extract from grass than from wood, the challenge is to make the entire process resource-efficient.
“We produce the pulp, but we don't have the equipment to make the textile fibres themselves. To produce the fibres, the pulp first has to be dissolved and then precipitated again. Viscose is a common textile fibre, but its production requires toxic chemicals. We don't want to use that process. Once the pulp has been dissolved, you need a spinneret, which you could perhaps compare to a potato ricer. And unfortunately, we don't have one of those in our lab,” says Diana Bernin.
“The next step is to produce pulp on a larger scale, but we can't do that at Chalmers. We are also continuing to optimise the dissolution process, which is the first step towards making fibres from our pulp. That is something we can do in our lab. If our pulp works with the more environmentally friendly textile fibre production process currently being developed by the Swedish company TreeToTextile, rather than the traditional viscose process, then perhaps we could have an environmentally friendly fibre in the future.”
There are also questions about the raw material itself.
“We also need to look at different types of grass, as well as how long the press cake can be stored and how it should be stored before being turned into dissolving pulp. Should it be dried or frozen? That also relates to the environmental and resource benefits. There are still many questions to answer before we have a process for producing dissolving pulp from press cake, and we look forward to finding the answers in the near future.”
Facts: From grass to multiple products
Grass and clover leys: Grass and clover grown on agricultural land, traditionally mainly for animal feed. Ley cultivation can also improve soil structure and increase soil organic matter.
Protein: Protein can be extracted from fresh grass and clover and used in animal feed, potentially replacing imported soy protein.
Energy: Residues left after protein extraction can be used to produce biogas.
Materials: The fibre-rich press cake contains cellulose that can serve as a raw material for bio-based products, including textile fibres. It also contains lignin and chlorophyll.
Green Valleys: A Swedish-Danish research and collaboration project focusing on green biorefineries, with demonstration facilities in Sweden and Denmark. Chalmers was one of several research and collaboration partners.
Land2Value: A follow-on project involving additional partners, including organisations from Norway. Diana Bernin's research group is participating, investigating how cellulose and other substances in press cake can be put to use.
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Leandro Cid Gomes
- Doctor, Applied Chemistry, Chemistry and Chemical Engineering
Leandro Cid Gomes
- Doctor, Applied Chemistry, Chemistry and Chemical Engineering
Diana Bernin
- Associate Professor, Applied Chemistry, Chemistry and Chemical Engineering
Diana Bernin
- Associate Professor, Applied Chemistry, Chemistry and Chemical Engineering
